Recuperator for combustion furnaces



Aug. 26, 1958 c. CONE ETAL RECUPERATOR FOR COMBUSTION FURNACES 3 Sheets-Sheet 1 Filed Nov. 1, 1954 -INVENTOR. Cara/l (one y VVll/iamH. Da/ley ATTO NE Aug. 26, 1958 c. CONE ETAL RECUPERATOR FOR COMBUSTION FURNACES a s. H v M60 E W M t C m W ,I A h m w mm a w 3 v. 8

Filed NOV. 1, 1954 *1 fllltt: 152mg RECUPERATOR non CDMBUSTION FURNACES Carroll Cone and William H. Dailey, Jr., Toledo, Ohio, assignors to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application November 1, 1954, Serial No. 466,038 19 Claims. (Cl. ans-20 This invention relates to an improved recuperator for combustion furnaces, and, more particularly, to such a recuperator constructed in a manner which minimizes stresses caused by differential expansion, which permits removal of various portions thereof without disturbance various parts are a major cause for failure, and any but minor repairs to the recuperator itself necessitate complete disassembly of the device and of refractory brick work associated therewith. Because metal parts of a recuperator are subjected to high temperatures during use, deterioration thereof occurs at a relatively rapid rate, with the result that, in previously known recuperators, the necessity for repairs has required frequent complete disassembly and reconstruction of the recuperator, and of refractory brick work associated therewith. The instant invention is based upon the discovery of a recuperator device wherein metal parts can be completely removed from the structure without the necessity for disturbing refractory brick work and other members associated therewith.

It is, therefore, an object of the invention to provide an improved recuperator for combustion furnaces.

It is a further object to provide improved controls for a recuperator.

Other objects and advantages of the invention will be apparent from the description which follows, reference being had to the accompanying drawings, in which- Fig. 1 is a view in elevation, with parts broken away to show internal structure, of a recuperator according to the invention;

Fig. 2 is a horizontal cross-sectional view along the line 22 in Fig. 1;

Fig. 3 is a vertical sectional view along the line 33 in Fig. 2;

Fig. 4 is a horizontal sectional view along the line 4-4 in Fig. 1;

Fig. 5 is a partially schematic diagram showing controls according to the invention; and

Fig. 6 is a fragmentary view in section showing a modified embodiment of a particularseal included in a recuperator according to the invention.

Referring now in more detail to the drawings, a recuperator according to the invention is indicated generally at 11 in Fig. 1. The recuperator 11 comprises an outer metal support shell 12, a refractory lining 13 for the shell 12, an inner metal liner 14, an intermediate metal 70 liner 15, and air passages 16 and 17. A metal shell 18 surrounds the lower extremities of the liners 14 and 15, below the lower limit of the shell 12, and forms a wind 2,849,218 Patented Aug. 26, 1958 box to which cooling air is admitted through a flanged duct 19.

In the specific embodiment of the invention shown the main structural support for the recuperator 11, including the shell 12 and the lining 13, comprises a ring support 20 welded or otherwise attached to a plurality of angle members 21 which are afixed to a main support structure or structures indicated generally at 22, which may comprise a plate member carried by suitably mounted I beams. A flange 23 structurally integral with the shell 12 is bolted to the support ring 20.

In operation, air to be preheated is passed through the flanged duct 19 into an annular space 26 between the shell 18 and the lower portion of the liner 15. The air passes around the'lower extremity of the liner 15 and upwardly through the air passage 17, around the upper extremity of the liner 15, and downwardly through the air passage 16. The preheated air leaves the recuperator 11 through a flanged duct 27 which communicates with the lower portion of the air passage 16. Combustion products from an associated combustion furnace, soaking pit, or the like, pass through a central passage 28 interior of a lower refractory lining 29 and of the inner liner 14.

Air is supplied through ducts 30 and 31 to a jet damper 32 to control the draft of the combustion products in the passage 28. Air supplied to the jet damper assembly 32 through the duct 30 is directed downwardly through orifices 33 (see Fig. 3) to retard the flow of combustion products, while air supplied through the duct 31 is directed upwardly through orifices 34 to aspirate combustion products from the passage 28.

Referring now more particularly to Fig. 3, the inner liner 14 carries, near its upper extremity, a main support ring 35 welded or otherwise rigidly attached thereto. The ring 35 is clamped between an upper clamping ring 36 and a canti-levered lower support plate 37. Through bolts 38 and nuts 39 attach the support plate 37 to a main support ring 40. The main support ring 40 is welded or otherwise rigidly attached to the shell 12. The upper clamping ring 36 is urged against the support ring 35 by nuts 41 threaded onto the through bolts 38. Sealing material 42 and 43, which can be, for example, asbestor gasket material, is clamped between the main support ring 40 and one extremity of the clamping ring 36, and between the ring 35 and the other extremity of the clamping ring 36 to provide a seal to prevent the escape of air being preheated from the passages provided therefor.

The jet damper assembly 32 and an upper stack member 45, the lower portion of which is shown, are clamped by through bolts 46 and 47 against the main support ring 41 and are free to be separated from the recuperator when the through bolts 46 and the nuts 47 are removed.

The intermediate liner 15 is supported near its lower extremity by a support ring 50 which is welded or otherwise rigidly attached thereto. The ring 50 is clamped against an inwardly extending portion 51 of the ring support 20 by a segmental ring 52, through bolts 53 and nuts 54. A seal 55, which may be asbestos gasket material, is provided between the ring 50 and the inwardly extending portion 51 of the ring support 20.

The lower portion of the wind box formed by the shell 13 and the inner liner 14 is sealed by an expansion seal indicated generally at 56. In the specific embodiment of the invention shown the expansion seal 56 comprises a continuous asbestos cloth gasket 57 held against the lower extremity of the shell 18 by a cylindrical mem ber 58 formed of perforate plate, and a ring angle 59. A ring 60 is attached to the ring angle 59 by through bolts 61 and nuts 62, and to a second ring angle 64 by through bolts 65 and nuts 66. Lugs 67 are welded or otherwise rigidly attached to the lower extremity of the inner liner 14. In one rotational position of the liner 14 the ring angle 64 contacts the lugs 67 so that the through bolts 65 and nuts 66 draw the ring 60 toward the lower extremity of-=the inner liner 14, making a gas-tight seal around an asbestos washer 68. The ring angle 64 is slotted so that in a second rotational position of the liner 14 the lugs 67 match the slots in the ring angle, and relative longitudinal movement between the entire expansion joint 56 and the inner liner 14 is possible.

When the recuperator is in operation, the inner liner 14 is heated to an elevated temperature. Since the support for the liner 14 is at its upper extremity, such expansion causes downward movement of the lower portion thereof, and of the expansion seal 56. The seal 56, however, is merely frictionally engaged against the shell 18, so that it is free to move without breaking the seal between it and the shell 18. Expansion of the inner liner does not appreciably affect the seal between the lower extremity thereof and the washer 68. The intermediate liner 15 is free to expand either upwardly or downwardly without interference with the operation of the recuperator.

The desired relative spacing between the inner liner 14 and the intermediate lining 15 is maintained, in the specific embodiment of the invention shown, by a plurality of spacing members 70 positioned in rings, for example, at five to ten foot intervals throughout the height of the recuperator, and welded in spaced relation ship around the interior surface of the intermediate liner 15. The specific inner liner 14 shown is cylindrical throughout its length, with only the ring 35 and the lugs 67 extending outwardly from the exterior thereof. As is indicated above, the lugs 67, in one rotational position of the liner 14, match notches in the ring angle 64 so that relative longitudinal movement between the ring angle 64 and the liner 14 is possible. In this same rotational position of the liner 14, the lugs 67 clear or pass be tween the spacing members 70, so that relative longitudinal movement between the inner liner and the intermediate liner 15 is also possible, and the former can be moved vertically from the position shown merely by removing the jet damper 32, the support plate 37 and the clamping plate 36.

With the upper stack member 45, the jet damper 32, the clamping ring 36, the support plate 37, and the inner liner 14 removed from the recuperator, longitudinal movement of the intermediate liner 15 is prevented only by the inwardly extending portion 51 of the ring 20, and the ring 52. The through bolts 53 and nuts 54 are accessible through ports closed by covers 72 (see Fig. 1). When it becomes necessary to remove the intermediate liner 15 it is necessary only to remove the covers "2 and nuts 54 and through bolt 53, after the recuperator has been disassembled to the extent indicated above, and the inner liner 14 removed, in order to permit longitudinal movement of the intermediate liner 15 to a position clear of the recuperator. The interior of the refractory 13 is then accessible for necessary repairs, as are the liners 14 and 15. After repairs have been made, the recuperator can be reassembled and returned to operation without the necessity for disturbing the shell 12 or the refractory lining 13.

It will be noted that numerous advantages inhere in the structural features of the recuperator 11 or an equivalent. The inner liner 14, which is subjected directly to ii the high temperature of the flue gases, is supported near its upper extremity, all other parts thereof being free to contract or expand with changes in temperature without setting up stresses in the recuperator. The only major force acting upon the inner liner is tensile, resulting from its weight. The ring 35, as well as the support ring 50 for the intermediate liner 15, is so supported that it can move radially to compensate for expansion and contraction. The spacing members 70 are shown as attached to the intermediate liner and spaced from the 4 inner liner to compensate for diiferential expansion, which may amount in practice to half an inch between the two.

The expansion seal 56 between the lower extremity of the liner l4 and the shell 18 and the seal around the support ring must of necessity be radially aligned with the hottest flue gases in order to obtain some of the advantages in relation to the liner 14 which have been discussed. The embodiment of the invention shown makes two provisions which minimize difliculties that might arise if the seal 56 were overheated. The lower refractory lining 29 separates radially both of these seals from the flue gases, and acts as insulation which minimizes the tendency for overheating. In addition, cold combustion air or other gas to be preheated in the recuperator is introduced directly into the annular space 26 where it cools both of these seals. The sealing material 42 and 43 at the upper extremity of the liner 14 is in a relatively cooler portion, so that all gas seals in the recuperator 11 are adequately protected against overheating.

An advantage of the recuperator 11 resides in the twopass path provided for air or other gas being preheated. It has been found in practice that radiant energy heats the intermediate liner 15 sufiiciently that heat transfer is from such liner to air in the passage 16. As a con sequence, the intermediate liner makes the recuperator 11 as eflicient as a longer device provided with only a single gas passage, and tends to minimize the maximum operating temperature and to increase equipment life.

Referring now to Fig. 5, various controls according to the invention are shown in connection with the recuperator 11. In normal operation, air is supplied to the flanged duct 19 from a blower 75, suitably driven as by an electric motor (not illustrated), and through a duct 76. Such air passes through the recuperator 11 where it is heated, as described. The heated air is then discharged from the recuperator through the flanged duct 27 and into a conduit 77, by which it is delivered as combustion air to pit burners 78. The rate at which combustion air is delivered to the burners 78 is controlled by a damper 79 which is regulated by a modulating air valve and proportioning gas valve 80. The valve 80 opens or closes the damper 79 in response to decreases or increases, respectively, in the temperature, as indicated by a thermocouple 81 in the soaking pit or other combustion zone 82, and proportions the rate of flow of gas or other fuel from a line 83 through a line 84 to the burners 78 to the rate of air flow.

A duct 85 interconnects the duct 76 and an auxiliary air duct 86, which can be a main header for supplying air to other soaking pits. A damper 87 in the duct 85 prevents, when in the closed position shown, the introduction of auxiliary air from the duct 86. However, when the pressure in the duct 76 as indicated through a conduit 88 drops below a predetermined minimum, a pressure responsive switchover 89 opens the damper 87 and simultaneously closes a damper 90 in the duct 76, so that auxiliary air from the duct 86 is supplied to the recuperator in the normal manner.

The control apparatus of Fig. 5 also includes a diluting conduit 92 through which air can be diverted from the duct 77 for admixture with flue gases when required. A damper 93 prevents such dilution unless the temperature in the recuperator, as indicated by a thermocouple 94 is higher than a predetermined maximum. A temperature operated bleed valve 95 measures the temperature indicated by the thermocouple 94 and, when such temperature is higher than the predetermined maximum, opens the damper 93 an amount which is a direct function of the measured temperature. When the control apparatus is set as shown in Fig. 5, opening the damper 93 as mentioned permits dilution of the flue gas and consequent cooling thereof, with air that has already passed through the recuperator 11. The use of such preheated air for dilution when the recuperator is in normal operation has the advantage of giving maximum cooling effect on metal parts from the volume of air that can be passed therethrough. When, therefore, as is sound practice, the blower is capable of delivering approximately the volume of air that the recuperator can handle, maximum cooling can be achieved from that volume of air by the arrangement shown.

It has been found that it is sometimes necessary to operate a soaking pit or other combustion furnace which is equipped with a recuperator according to the inven tion even when the recuperator is not operative, for example beause of needing repair. The control apparatus of Fig. 5 provides a bypass conduit 96 provided with a damper 97 which enables operation of the soaking pit 82 even when the recuperator M is temporarily unserviceable. To operate the soaking pit, bypassing the recuperator 11, the damper 97 is opened, and a damper 98 in the duct 76 is closed, so that air supplied either by the blower 75 or, as described, through the ducts 86 and 85, is introduced through the conduit 96 into the duct 7'7. Such air is then supplied to the burners 78, its passage through the recuperator being prevented by the damper 98. Air inside the heating passages in the recuperator is stagnant under these conditions, with the result that the temperature indicated by the thermocouple 94 is essentially the flue gas temperature. The temperature operated bleed valve 95, therefore, opens the damper 93 an amount suificient to drop the flue gas to a temperature at which it does not damage the recuperator.

The ducts 30 and 31l for supplying air to the jet damper 32 connect with the duct 76. A pressure operated control 99 automatically positions dampers ltttl and 161 to compensate for changes in flue gas pressure upstream from the jet damper, for example, to compensate for pressure changes in the soaking pit 82, as transmitted to the control 99 through a line ltlZ. When the pressure in the soaking pit 82 is below a predetermined minimum, the damper ltltl is closed by the control 99, and the damper 101 is opened an amount which is an inverse function of the indicated pressure. When the pressure in the soaking pit 82 is above a predetermined maximum, the damper 101 is closed, and the damper ltltl is opened an amount which is a direct function of pressure in the soaking pit. The orifices 33 and 34 (see Fig. 3) of the damper 32 are arranged in annular rings surrounding the flue gas passage. They require no control that must be near the recuperator, as even the dampers W0 and 161 can be located at any points in the ducts 3t and 30, respec-- tively. The use of a plurality of aspirating jets 34, each of small diameter, is advantageous over a single large jet because of the ease of control, and also because only a short stack is required thereabove. in the specific apparatus shown the jets are about /2 inch in diameter, only approximately a four foot stack being required thereabove for venting action.

It will be observed that the jet damper is operable even when the recuperator is being bypassed, as above described. Air pressure is available in the duct '76 at all times for operation thereof.

A modified embodiment of the seal 56 (Fig. 3) is shown in Fig. 6. This seal, also indicated generally by the numeral 56, includes the ring 60, the ring angle or attached thereto by through bolts 65 and nuts 66, lugs 6'7 attached to the lower extremity of the liner l4, and the washer 68 shown in and described in reference to Fig. 3. A seal between the shell 18 and the ring of is effected by a neoprene sheet 103 which, in the specific embodiment shown, is attached to the exterior of the shell 13 by through bolts 1% and nuts lilo", and to the ring on by through bolts 1% and nuts M7.

It will be apparent that various changes and modifications can be made from the specific details of the invention disclosed and shown in the accompanying drawings without departing from the spirit of the attached claims, and that, in its essential details, the invention comprises various controls as described, and a combustion furnace recuperator having a generally vertical inner liner for receiving flue gases exhausted from a furnace and for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of the inner liner, and forming, with the inner liner a gas heating passage, an inlet box for supplying gas to one end of the passage, discharge means for receiving gas from the other end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means, such apparatus being characterized by including support means for the inner liner consisting of an upper hanger and spacing lugs between the inner liner and the intermediate liner, the upper hanger comprising at least one support attached to the upper end of the inner liner, a cooperating bearing member, and releasable means for clamping the support against the bearing member, in at least one rotational position of the inner liner, upward movement thereof until it clears the re cuperator being unobstructed by the spacing lugs.

We claim:

1. A combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communciating with the first gas passage, an inlet box for supplying gas to one end of the first passage, a refractory lining interior of a part only of said inner liner adjacent its inlet end and spaced therefrom, and radially aligned with said inlet box, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, a lower sealing member comprising releasable clamping means engaging, and compressing a gasket in sealing relationship with, the lower extremity of said inner liner, and means forming a seal between said last-named means and said inlet box, support means for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached to the upper end of said inner liner, a cooperating hearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members, and support means for said intermediate liner consisting of a lower hanger, said lower hanger comprising at least one supporting member attached to said intermediate liner, at least one cooperating bearing plate, and releasable means for clamping said supporting member against said hearing plate.

2. A combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communicating with the first gas passage, an inlet box for supplying gas to one end of the first passage, a refractory lining interior of a part only of said inner liner adjacent its inlet end and spaced therefrom, and radially aligned with said inlet box, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, means forming a gas-tight seal between the lower extremities of said inner liner and of said inlet box, support means for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached to the upper end of said inner liner, :1 cooperating bearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members, and support means for said intermediate liner consisting of a lower hanger, said lower hanger comprising at least one supporting member attached to said intermediate liner, at least one cooperating bearing plate, and releasable means for clamping said supporting member against said bearing plate.

3. A combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communciating with the first gas passage, an inlet box for supplying gas to one end of the first passage, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, means forming a gastight seal between the lower extremities of said inner liner and of said inlet box, support means for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached to the upper end of said inner liner, a cooperating bearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members, and support means for said intermediate liner consisting of a lower hanger, said lower hanger comprising at least one supporting member attached to said intermediate liner, at least one cooperating bearing plate, and releasable means for clamping said supporting member against said bearing plate.

4. A combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for'discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communicating with the first gas passage, an inlet box for supplying gas to one end of the first passage, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, a lower sealing member comprising releasable clamping means engaging the lower'extremity of said inner liner, and means forming a gas seal between said last-named means and said inlet box, support means for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached to the upper end of said inner liner, a cooperating bearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members, and support means for said intermediate liner consisting .8 p of a lower hanger, said lower hanger comprising at least one supporting member attached to said intermediate liner, at least one cooperating bearing plate, and releasable means for clamping said supporting member against said bearing plate.

5. A combustion furnace recuperator comprising a generally vertical Iinner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming, with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communicating with the first gas passage, an inlet box for supplying gas to one end of the first passage, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, means forming a gas tight seal between the lower extremities of said inlet box and of said inner liner, support mepns for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached to the upper end of said inner liner, a cooperating bearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members.

6. A combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of said inner liner, including the inlet end thereof, and forming, with said inner liner, a first gas heating passage, an outer supporting shell forming, with said intermediate liner, a return gas passage communicating with the first gas passage, an inlet box for supplying gas to one end of the first passage, discharge means for receiving gas from one end of the return passage, means for supplying gas to said inlet box, means for conducting gas from said discharge means, a lower sealing member comprising releasable clamping means engaging the lower extremity of said inner liner, and means forming a seal between said last-named means and an interior wall of said inlet box, support means for said inner liner consisting of an upper hanger, and spacing members between said inner liner and said intermediate liner, said upper hanger comprising at least one support attached 'to the upper end of said inner liner, a cooperating bearing member releasably attached to said supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of said inner liner, upward movement thereof until it clears the recuperator is not obstructed by said sealing member and spacing members.

7. In a combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an outer supporting shell surrounding at least a substantial portion of the inner liner, and forming, with the inner liner, a gas heating passage, an inlet box for supplying gas to one end of the gas passage, discharge means for receiving gas from an opposite end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means, the improvement which includes a sealing member comprising releasable clamping means engaging an extremity of the inner liner which is free to move longitudinally to compensate for contraction and expansion of the liner, and means forming a seal in a plurality of relative positions between said releasable clamping means and an interior wall of the inlet box.

8. In a combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an outer supporting shell surrounding at least a substantial portion of the inner liner, and forming, with the inner liner, a gas heating passage, an inlet box for supply ing gas to one end of the gas passage, discharge means for receiving gas from an opposite end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means, the improvement which includes an intermediate liner separating the gas heating passage into a first passage communicating with the inlet box and a second passage radial to the first end communicating with the discharge means, support means for the inner liner consisting of an upper hanger, and spacing members between said intermediate liner and the inner liner, said upper hanger comprising at least one support attached to the upper end of the inner liner, a cooperating bearing member releasably attached to the supporting shell, and releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of the inner liner, upward movement thereof until it clears the recuperator is not obstructed by said spacing members.

9. In a combustion furnace recuperator comprising a generally vertical inner liner having an inlet end for receiving flue gases exhausted from a furnace and an exhaust end for discharging such gases to the atmosphere, an outer supporting shell surrounding at least a substantial portion of the inner liner, and forming, with the inner liner, a gas heating passage, an inlet box for supplying gas to one end of the gas passage, discharge means for receiving gas from an opposite end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means, the improvement which includes upper hanger support means for 'the inner liner adjacent the discharge end thereof and comprising at least one support attached to the upper end of the inner liner, a cooperating bearing member releasably attached to the supporting shell, an releasable means for clamping said support against said bearing member, wherein, in at least one rotational position of the inner liner, upward movement thereof until it clears the recuperator is not obstructed.

10. A combustion furnace recuperator comprising a liner for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, means surrounding the liner and forming therewith a combustion air heating passage, a source for combustion air under pressure, means including an inlet box for supplying combustion air to one end of the passage, discharge means for receiving air from the other end of the passage, and duct means for conducting air from the discharge means to an associated burner, characterized by a control system including an auxiliary source for combustion air under pressure, conduit means interconnecting said auxiliary source and the duct means, means for preventing the flow of air through said conduit means when combustion air is flowing through the air heating passage, diluting conduit means for diverting air from the duct means for admixture with flue gases exhausted from the furnace, means for preventing the flow of combustion air through the air heating passage, means for preventing the flow of air through said diluting conduit means when the temperature of flue gases in the recuperator is less than a predetermined minimum, and means for varying the obstruction to flow of air in said diluting conduit means as an inverse function of temperature of flue gases in the recuperator when such temperature is above the predetermined minimum.

ll. A combustion furnace recuperator comprising a liner for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, means surrounding the liner and forming therewith a combustion air heating passage, a source for combustion air under pressure, means including an inlet box for supplying combustion air to one end of the passage, discharge means for receiving air from the other end of the passage, and duct means for conducting air from the discharge means to an associated burner, characterized by a control system including diluting conduit means for diverting air from the duct means for admixture with flue gases exhausted from the furnace, means for preventing the flow of air through said diluting conduit means when the temperature of flue gases in the recuperator is less than a predetermined minimum, and means for varying the obstruction to flow of air in said diluting conduit means as an inverse function of temperature of flue gases in the recuperator when such temperature is above the predetermined minimum.

l2. In a combustion furnace recuperator comprising a conduit for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, a shell surrounding at least a substantial portion of the conduit, including the end thereof for receiving flue gases, and forming, with the conduit, a combustion-air heating passage, an inlet box for supplying combustion air to one end of the passage, discharge means for receiving combustion air from the other end of the passage, means for supplying combustion air to the inlet box, and means for conducting combustion air from the discharge means to an associated burner, the improvement which includes valve means for obstructing the flow of combustion air from the discharge means to an associated burner, control means responsive to changes in temperature in the combustion zone of the furnace for positioning said valve means and effective to vary the resistance to flow of combustion air as a direct function of combustion zone temperature, and means supplying fuel to the burner at a rate which is a direct function of the rate at which air is supplied thereto.

13. In a combustion furnace recuperator comprising a conduit for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, a shell surrounding at least a substantial portion of the conduit, including the end thereof for receiving flue gases, and forming, with the conduit, a gas heating passage, an inlet box for supplying gas to one end of the passage, discharge means for receiving gas from the other end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means to an associated burner, the improvement which includes means for directing heated air discharged from the recuperator for admixture with flue gases received by the recuperator, means for preventing the admixture of such air with flue gases when the temperature of the former is below a predetermined minimum, and means for varying the obstruction to flow of such preheated air as an inverse function of the temperature thereof when such temperature is above the predetermined minimum.

14. In a combustion furnace recuperator comprising an inner liner for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, an intermediate liner surrounding at least a substantial portion of the inner liner, including the end thereof for receiving flue gases, and forming, with the inner liner, 2. gas heating passage, means including an inlet box for supplying gas to one end of the passage, discharge means for receiving gas from the other end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means to an associated burner, the improvement which includes a damper control having a plurality of annularly disposed orifices for directing gas interiorly of the discharge end of the inner liner generally in opposition to the direction of flue gas movement therein, and a plurality of annularly disposed orifices for so directing gas generally parallel to the direction of flue gas movement therein, means for supplying gas to said damper control, and means responsive to changes in pressure in the flue gas system ofsthe furnace, upstream from said damper control, for regulating the operation thereof, and effective when such pressure is less than a predetermined minimum to prevent the discharge of gas through said orifices generally parallel to the direction of flue gas movement and to vary .the obstruction to the discharge of gas through said orifices .in opposition to the direction of flue gas movement as an inverse function of such pressure, and effective, when such pressure is higher than a predetermined maximum, to prevent the discharge of gas through said orifices generally opposed to the direction of flue gas movement, and to vary the obstruction to the discharge of gas through .said orifices generally parallel to the direction of flue gas movement as a direct function of such pressure.

15. In a combustion furnace recuperator comprising an inner liner for receiving flue gases exhausted from a furnace and discharging such gases to the atmosphere, an intermediate liner surroundingat least a substantial .portion of the inner liner, including the end thereof for receiving flue gases, and forming, with the inner liner, a gas heating passage, means including an inlet box for supplying gas to one end of the passage, dischargemeans for receiving gas from the other end of the passage, means for supplying gas to the inlet box, and means for conducting gas from the discharge means to an associated burner, theimprovement which includes a damper control having a plurality of annularly disposed orifices for directing gas interiorly of the discharge end of the inner liner generally parallel to the direction of flue gas movement therein, means for supplying gas to said damper control, means responsive to changes in pressure in the *flue gas system of the furnace, upstream from said damper control, for regulating the operation thereof, and effective when such pressure is less than a predetermined minimum to prevent the discharge of gas through said orifices, and effective, when such pressure is higher than .a predetermined maximum, to vary the obstruction to the discharge of gas through said orifices.

l6. Recuperator apparatus for transferring heat from flue gas discharging from a vertically opening flue of an associated furnace which comprises: a vertical flue gas pipe aligned with the opening of said associated furnace flue; sealing means connecting the lower .end of said pipe to the opening to confine flue gases passing therethrough and allow vertical relative movement of said flue gas pipe lower end; an outer pipe forming with said flue gas pipe a fluid heating passage; means for supplying fluid to one end of said passage; means for discharging fluid at the other end of said passage; a first annular flange extending from the upper end of said flue gas pipe, said first annular flange having an outside diameter substantially less than the inside diameter of said outer pipe; a pair of annular flanges extending from said outer pipe, said pair of flanges having an inside diameter substantially greater than the outside diameter of saidflue gas pipe, said pair of flanges also cooperatively engaging said first flange to support said flue gas pipe in a manner which permits radial movement thereof and to form sealing means for the upper end of said fluid heating passages.

17. Recuperator apparatus for transferring heat from flue gas discharging from a vertically opening flue of an associated furnace which comprises: a vertical flue gas pipe aligned with the opening of said associated furnace flue; sealing means connecting the lower end of said pipe to the opening to confine flue gases passing therethrough and allow vertical relative movement of said flue gas pipe lower end; at least one concentrically positioned intermediate pipe surrounding at least a substantial portion of the flue gas pipe; a concentrically positioned outer pipe surrounding the outermost intermediate pipe, said outer, intermediate and flue gas pipes being in spaced relation to one another -to define a series of fluid passages therebetween; support means for each of said intermediate and said flue gas pipes comprising a first radial flange extending from said intermediate and flue gas pipes, a second radial flange extending from said outer pipe, said first and second flanges cooperatively engaging each other to support said intermediate and said flue gaspipes in a manner which seals the joint therebetween and permits radial movement thereof without interfering with the fluid flow through said series of passages; and means forming a fluid inlet to said series of passages at one end thereof and a fluid outlet at the other end thereof.

18. Recuperator apparatus for transferring heat from flue gas discharging from a vertically opening flue of an associated furnace which comprises: a vertical flue gas pipe aligned with the opening of said associated furnace flue; sealing means connecting the lower end of said pipe to the opening to confine flue gases passing therethrough and allow vertical movement of said flue gas pipe; an intermediate pipe surrounding at least a substantial portion of said flue gas pipe, and forming with said flue gas pipe, a first fluid heating passage; an outer pipe forming with said intermediate pipe, a return fluid passage communicating with the first fluid passage; means for supplying fluid to one end of the first passage; means for discharging fluid from one end of the return passage; support means for said flue gas pipe attached to said outer pipe for cooperative engagement with the upper end of said flue gas pipe in a manner which permits lateral expansion of said flue gas pipe relative to said support means, said support means also forming a seal between said flue gas pipe and said outer pipe; and intermediate pipe support means attached to said outer pipe for co-operative engagement with said intermediate pipe in a manner which permits lateral expansion of said intermediate pipe relative to said intermediate pipe support means, said intermediate pipe support means also forming a seal between said intermediate.

pipe and said outer pipe.

19. Recuperator apparatus for transferring heat from flue gas discharging from a vertically opening flue of an associated furnace which comprises: a vertical flue gas pipe aligned with the opening of said associated furnace flue; sealing means connecting the lower end of said pipe to the opening to confine flue gases passing therethrough and allow vertical movement of said flue gas pipe; an intermediate pipe surrounding at least a substantial portion of said flue gas pipe, and forming with said flue gas pipe, a first fluid heating passage; an outer pipe forming with said intermediate pipe, a return fluid passage communicating with the first fluid passage; means for supplying fluid to one end of the first passage; means for discharging fluid from one end of the return passage; support means for said flue gas pipe comprising a first radial flange extending from the upper end of said flue gas pipe, and a second radial flange extending from said outer pipe for slidable yet scalable engagement with said first radial flange; and intermediate pipe support means comprising a third radial flange extending from said intermediate pipe, and a fourth radial flange extending from said outer pipe for slidable yet scalable engagement with said third radial flange.

References Cited in the file of this patent UNITED STATES PATENTS 2,639,910 Cone et al May 26, 1953 2,686,048 Peck et a1 Aug. 10, 1954 FOREIGN PATENTS 590,382 Great Britain July 16, 1947 

